You are using an unsupported browser, old browsers can put your security at risk. Please upgrade to a supported browser.

OK ESA uses cookies to track visits to our website only, no personal information is collected. By continuing to use the site you are agreeing to our use of cookies. Find out more about our cookie policy.

Pointing calibration and performance

Paper on the pointing system of the HSO, including a description, calibration, performance and improvements (Sánchez-Portal et al, 2014, Experimental Astronomy, Volume 37, Issue 2, pp.453-479). Can be found at the Experimental Astronomy web page or astro-ph

Spacecraft/instrument alignment matrix historical record

The table below shows the recent SIAM update history (from OD299 onwards) showing the SIAM file used in up-link and the suggested down-link one. The SIAM matrices are a component of the auxiliary context inside the observation context.

OD range

SIAM used in uplink

SIAM used in pipeline

Suggested reprocessing SIAM

Comment

299

0122_0001

0122_0001

0341_0001

The temperature of the STR CCD was lowered to -10 degC to carry out the pointing calibration campaign at the new reference temperature. Raised again at the following DTCP

300-319

0122_0001

0122_0001

0122_0001

STR CCD reference temperature set back to +13 degC

320-329

0320_0001

0341_0001

0341_0001

STR CCD temperature lowered permanently to -10degC. The SIAM used in uplink was computed using incorrect offsets (reversed signs in both Y and Z offsets) resulting in target misalignment of some 10 arcsec. The use of a correct SIAM in downlink fixes the astrometry problems

330-339

0320_0002

0341_0001

0341_0001

New SIAM computed with correct Y, Z offsets

341-342

0341_0001

0341_0001

0341_0001

Some refinements based on pointing measurements carried out in OD330

343-353

0320_0002

0341_0001

0341_0001

354-...

0341_0001

0341_0001

0341_0001

A quite complete summary of the pointing performances during operations can be found here. See also the Experimental Astronomy paper. For information on current pointing figures based on ground-reprocessing, see here.

A technical note on the Absolute Pointing Error (the estimation of its 68th percentile from calibration observations): CAS_APE_calc_1p1.pdf

Spacecraft health monitoring

Spacecraft temperature tracking

The figure below shows the temperature evolution of the main mirror (M1), the Cyo Vacuum Vessel (CVV) and the Sun-Shade (SS) of the Herschel Spacecraft since OD 50 (2009-07-02) to OD 630 (2011-02-02) plus M1 and CVV comparison to OD 1445 (2013-04-29):

Radiation environment tracking

The radiation monitor on-board Herschel is called SREM for Standard Radiation Environment Monitor. SREM raw and calibrated data products are delivered with the Herschel observations as part of the auxiliary context, inside the observation context. The SREM units detect and count electrons, protons and cosmic rays with a coarse spectral resolution and ±20◦ angular resolution. The measurements are based on silicon diodes polarized in reverse by a high voltage. The SREM consists of three detectors, D1, D2 and D3, mounted in two heads. One head consists of a single silicon diode (D3) and its main entrance window is covered with an aluminium plate of 0.7mm, defining a lower energy threshold of ~0.5MeV for electrons and ~10MeV for protons. The other head uses to silion diodes (D1/D2) arranged in a telescope configuration. The main entrance window is covered with an aluminum plate of 2mm providing a threshold of 1.5MeV for electrons and 20MeV for protons.

SREM calibrated 5-minutes-rebinned counts from the 30th of October 2009 to 29 April 2013, a second plot zooming on the large solar Flares on the 23rd Jan and on the 7th of March 2012, the largest ever in the history of the Herschel mission: